Expired hair dye may not work effectively and may cause unwanted side effects to your hair or scalp. There is no evidence that old hair dye is dangerous to use, but it may cause chemical burns on the scalp or leave your hair unevenly colored. The most likely effect of using old hair dye is that it won’t work or that your hair will be a darker shade than you were anticipating. In some instances, you may get uneven color results. Here are some of the other things to watch out for if you have hair dye that’s potentially expired:

• Bad smell: Once opened, any type of hair dye may become contaminated by bacteria or fungi. If this occurs, a bad smell may result. Opened hair dye is only safe to use for a limited window of time.

• Change in consistency: If a product that was supposed to have a thick consistency has become runny, you should not be using it anymore. In addition, if you see that the hair dye has separated, throw it away immediately.

• Allergic reactions: Hair dyes, like everything else, have an expiration date. If you do not ensure proper hair dye storage, the solutions can quickly go bad, and using them after they expire may damage your locks. Using expired hair dye may cause allergic reactions, such as a burning sensation, scalp itchiness, hair loss, and other negative effects.

It is best to be aware of and practice hair dye safety. If you have expired hair dye, it is recommended to check the date printed on the bottle or squeeze tube. If that date has passed, then it’s best to throw the dye away.